Tito Ortiz went behind Jenna Jameson's back to file for a restraining order against the porn legend's close friend ... telling filthy lies to the judge in the process -- so says the friend.
TMZ broke the story ... Tito filed the restraining order docs last week, asking an O.C. court to protect him and Jenna from Shana Burroughs, claiming Shana is a drug-fueled crazy person who stalks the couple and scares their children.
But Shana tells TMZ, she and Jenna have been close pals for years -- long before Jenna met Tito -- and now, the MMA fighter's gunning to sabotage their friendship.
According to Shana, Tito has it out for her because she refused to back him in 2010 when he went public with Jenna's drug problems.
Shana says Jenna had no idea Tito even filed restraining order docs until she confronted her.
As for Tito's drug allegations ... Shana insists she never brought a single drug (prescription or otherwise) into Jenna's home. She tells us, Jenna's DUI was not Shana's fault.
A hearing on the restraining order is scheduled for June 15.